Adrenergic mechanisms in the bullfrog and turtle

¹ Department of Physiology, University of Minnesota, Minneapolis, Minnesota

Epinephrine and norepinephrine contents of tissues and perfusates have been measured by fluorimetric methods to ascertain which catecholamine is the sympathetic transmitter in bullfrogs and turtles. Except for adrenal and sympathetic chain, the predominant catecholamine in bullfrogs is epinephrine. In snapping turtles, norepinephrine predominates. During perfusion of bullfrog heart or liver without stimulation, only traces of catecholamine appear in perfusates, whereas during sympathetic nerve stimulation a large output of epinephrine occurs. In the bullfrog epinephrine rather than norepinephrine seems to be the sympathetic mediator. The situation may be the reverse in the turtle. Environmental temperature did not alter bullfrog tissue catecholamine. Cardiac sympathetic denervation did not decrease myocardial catecholamine within 6 weeks at low temperatures, but in animals maintained at 20 C survival was not achieved. Epinephrine levels in bullfrog ventricle were not lowered by 5 hr of contractions induced by electrical stimulation at 30/min compared with controls in arrest. The fact that myocardial catecholamine stores are not depleted by contractile activity may result either from absence of utilization or from equivalence between breakdown and synthesis.

Key Words: heart catecholamine • bullfrog organ catecholamine content • liver catecholamine content • brain catecholamine content • adrenal catecholamine content • heart work and catecholamine depletion

Submitted on April 26, 1965

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